The complexity of the regulation of differentiation and proliferation of and by hematopoietic cells is becoming increasingly apparent as the list of factors which are isolated which control these events continuously increases. For the most part, these factors are present in extraordinarily minute amounts in conjunction with numerous other proteins which serve a wide variety of functions. Factors which have been isolated and demonstrated to have activity include polypeptides and proteins such as Y-interferon, platelet-derived growth factor, colony stimulating factor, interleukin-2, erythropoietin, as well as numerous other lymphokines. There is substantial interest in the isolation, purification and characterization of these blood components as well as efficient preparation of large amounts of these peptides because of their possible use in cancer treatment, as well as their use in studying diseases such as cancer.